Nitrogen bridgehead compounds. Part 29. Tautomerism and Z–E isomerism of ethyl 9-aminomethylene-4-oxo-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidine-3-carboxylates and their homologues

6‐Methyl‐6,7,8,9‐tetrahydro‐4H‐pyrido[1,2‐a]pyrimidin‐4‐ones 1‐5 were subjected to Vilsmeier‐Haack acylation with complexes of phosphoryl chloride and different amides. Acylation at position 9 of the pyridopyrim‐idines was successful with the iminium salt formed in situ from N‐formylpiperidine, N‐methylformanilide or N,N‐diethylbenzamide, but unsuccessful with the iminium salt formed from N,N‐diethylacetamide or N,N‐di‐ethylisobutyramide, respectively. The iminium salt formed from formanilide, N‐methylpyrrolidinone or formamide reacted only with those tetrahydropyridopyrimidinones which contain a strongly electronegative substituent (e.g. CN or CO2Et) in position 3. With the latter derivatives, the 9‐phenylaminomethylene group could be introduced using N,N‐diphenylformamide or in a “one‐pot” procedure with aniline and triethyl orthoformate. Ethanolysis of 9‐N‐methyl‐N‐phenylaminomethylene derivatives 15 and 19 afforded 9‐ethoxy‐methylene compounds 26 and 27 in the presence of hydrogen chloride. The structures of the 9‐substituted 6‐methyltetrahydropyridopyrimidin‐4‐ones 14‐25 were elucidated by means of uv, 1H and 13C nmr spectroscopy. 9‐Piperidinomethylene 14, 9‐(N‐methyl‐N‐phenylaminomethylene 15‐19 and 9‐(N‐methyl‐2‐pyrrolidinylidene) 21 derivatives exist as E geometric isomers. 9‐Phenylaminomethylene‐6‐methyl‐4‐oxo‐6,7,8,9‐tetra‐hydro‐4H‐pyrido[1,2‐a]pyrimidine‐3‐carbonitrile 20 displays a solvent‐dependent E‐Z isomerism. The bis‐compound 25 contains both E and Z geometric exo C  CH double bonds. 9‐Benzoyl derivatives 23 and 24 exist predominantly as the 1,6,7,8‐tetrahydropyridopyrimidin‐4‐one tautomer.

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Nitrogen bridgehead compounds. Part 77. Addition reaction of 9‐methylene‐6,7,8,9‐tetrahydro‐4H‐pyrido[1,2‐a]pyrimidin‐4‐ones

Tóth

Janke

Hermecz

et al. 1990

Journal of Heterocyclic Chem

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Addition of bromine or thioacetic acid onto 6‐methyl‐9‐methylenetetrahydro‐4H‐pyrido[1,2‐a]pyrimidin‐4‐ones is stereoselective and gives the cis 6‐Me,9‐CH substituted products. Addition is also stereoselective in respect to the C(9) and C(10) centers, and gives as the primary product the erythro diastereomer, which may then undergo epimerization to the threo isomer. Relative configuration and predominant conformation of the products were determined by 1D and 2D nmr methods.

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Nitrogen bridgehead compounds. Part 29. Tautomerism and Z–E isomerism of ethyl 9-aminomethylene-4-oxo-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidine-3-carboxylates and their homologues

Abstract: Nach 1H‐ und 13C‐NMR‐Untersuchungen liegen die Ester (I) und das Homologe (V) (n=0) in der E‐Form vor, das Homologe (V) (n=2) dagegen als Z,E‐Gemisch.

Cited by 8 publications

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ChemInform Abstract: Nitrogen Bridgehead Compounds. Part 29. Tautomerism and Z‐E Isomerism of Ethyl 9‐Aminomethylene‐4‐oxo‐6,7,8,9‐tetrahydro‐4H‐pyrido[1,2‐a]pyrimidine‐3‐carboxylates and Their Homologues.

ChemInform Abstract: Nitrogen Bridgehead Compounds. Part 29. Tautomerism and Z‐E Isomerism of Ethyl 9‐Aminomethylene‐4‐oxo‐6,7,8,9‐tetrahydro‐4H‐pyrido[1,2‐a]pyrimidine‐3‐carboxylates and Their Homologues.

Nitrogen bridgehead compounds. Part 50. Vilsmeier‐haack acylation of 6,7,8,9‐tetrahydro‐4H‐pyrido[1,2‐a]pyrimidin‐4‐ones, Part 5

Nitrogen bridgehead compounds. Part 77. Addition reaction of 9‐methylene‐6,7,8,9‐tetrahydro‐4H‐pyrido[1,2‐a]pyrimidin‐4‐ones

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